MICELLAR EFFECTS ON THE NITROSATION BY PIPERIDINES BY 2-BROMOETHYL NITRITE AND 1-PHENYLETHYL NITRITE IN BASIC-MEDIA

The nitrosation of piperidine (P), 2-methylpiperidine (2-MP), and 4-me thylpiperidine (4-MP) by 2-bromoethyl nitrite (BEN) and 1-phenylethyl nitrite (PEN) is kinetically studied in basic media and in the presenc e of tetradecyltrimethylammonium bromide (TTABr) and sodium dodecyl su lfate (SDS) micelles. In the case of cationic micelles of TTABr and wi th BEN as the nitrosating agent, the results are explained assuming th at only the alkyl nitrite is distributed between the aqueous and the m icellar pseudophases, whereas the reaction takes place in water. When the nitrosating agent is 1-phenylethyl nitrite, reaction in the micell ar pseudophase is also observed. This result is evidence for the kinet ic relevance of stoichiometrically negligible amounts of hydrophilic r eagents in the micelles in the case of reactions involving highly hydr ophobic substrates. The previous estimation, by indirect methods, of t he binding constant of the unprotonated amine to the micelles allows a quantitative estimation of the rate constants in the micellar pseudop hase, which could be compared with those in water. With anionic micell es of SDS, the results are analyzed by using the simple pseudophase io n-exchange (PPIE) model taking into account the partitioning of alkyl nitrites between the micellar and aqueous pseudophases and, simultaneo usly, the change in the basic ionization equilibria of the amine, beca use of the competition between the ammonium ion of the amine and Na+, for binding to the micelle. The electrostatic interaction of protonate d amine with the micellar surface reduces the quantity of total unprot onated amine, the reactive form. Rate constants for the reaction in th e micellar pseudophase and in water, obtained from the kinetic analysi s, are reported and discussed. Binding constants of the unprotonated a mine to the SDS micelles, as well as the ion exchange constants betwee n the counterions of the micelle, Na+, and the ammonium ions of the co rresponding amine, were previously determined from absorbance measurem ents.